<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        //用户输入一个数，  计算 1 到这个数的累加和
        let num = +prompt('请输入一个数')
        let sum = 0
        for (let i = 1; i <= num; i++) {
            sum += i
        }
        console.log(sum)




    </script>

</body>

</html>